This invention pertains to highly dispersed anion-modified iron oxide slurry catalysts, having high surface area and high catalytic activity for hydroconversion reactions. It pertains particularly to such dispersed iron oxide catalysts which are synthesized by rapid precipitation from saturated aqueous solutions of iron salts in presence of selected anions, including molybdate (MoO.sub.4.sup.2-), phosphate (PO.sub.4.sup.3-), sulfate (SO.sub.4.sup.2-) or tungstate (WO.sub.4.sup.2-), and are promoted by the addition of small amounts of an active hydrogenation metal including cobalt, molybdenum, nickel, and tungsten. Such dispersed catalysts are useful for hydroconversion of carbonaceous feed materials such as coal, heavy petroleum resids, and other high molecular weight hydrocarbons such as waste plastics to produce desirable value-added low-boiling hydrocarbon liquid products.
The use of various iron containing compounds such as pyrites (FeS.sub.2) and red mud (Fe.sub.2 O.sub.3) as catalysts for coal hydrogenation and liquefaction processes has been well known for many years. Such particulate iron compounds were usually added in small amounts to a coal-oil slurry feedstream upstream of a catalytic reactor operated at elevated temperature and pressure conditions. However, because of the generally low effectiveness of such known catalysts primarily due to their low initial surface areas and inability to provide high levels of dispersion (number of catalyst particles per unit reacting volume, a direct measure of how finely divided the catalyst is) under reaction conditions, catalytic hydroconversion processes for coal and heavy petroleum feedstocks which have been developed during the past 30 years have usually utilized particulate (extrudate) supported type catalysts having small amounts of one or more active promotor metals such as cobalt, molybdenum or nickel deposited on an inert support material such as alumina or silica. Some examples of such extrudate supported catalysts are disclosed by U.S. Pat. No. 3,630,888 to Alpert et al, U.S. Pat. No. 4,294,685 to Kim et al.; and U.S. Pat. No. 4,424,109 to Huibers et al. Such extrudate supported catalysts are used in either downflow fixed bed reactors or in upflow ebullated bed reactors each maintained at desired conditions of temperature, pressure and space velocity.
Although such particulate extrudate supported type catalysts such as cobalt-molybdenum or nickel-molybdenum deposited on alumina or silica support and catalytic hydroconversion processes using the supported catalysts have provided good results for hydrogenation and hydroconversion of coal and heavy oil feed materials, some disadvantages of such particulate supported type catalysts are their relatively poor contact with the feed materials primarily due to the pore-diffusional limitations and rapid deactivation caused by deposition on the catalyst of coke and metal contaminants such as iron, nickel, and vanadium contained in the feeds. U.S. Pat. No. 4,136,013 to Moll et al. discloses an emulsion-type metal catalyst useful for hydrogenation processes, but it also has disadvantages of low catalytic activity and high catalyst usage. At the levels of catalyst usage disclosed in the Moll et al. patent, the catalyst cost becomes prohibitive unless the catalyst is recovered from the unconverted material and reused. U.S. Pat. Nos. 4,134,825 and 4,077,867 to Bearden et al. disclose an in-situ formed metal-carbon containing dispersed slurry catalyst, called `M-Coke` for hydroconversion of coal, heavy oil, and mixtures thereof. These catalysts of Bearden et al. are primarily based on molybdenum which is significantly more expensive than iron and which is the principal component of the catalyst of the present invention. Also, disposal of used molybdenum catalyst is not environmenatlly as benign as that of an used iron catalyst. U.S. Pat. No. 4,486,293 to D. Garg disclosed a co-catalyst combination of iron and Group VI or VIII non-ferrous metal for liquefaction of coal in a hydrogen-donor solvent using water soluble salts of the co-catalyst metals. It is known that catalysts formed from the water-soluble precursor salts often undergo sintering under coal liquefaction conditions and lack a high degree of dispersion necessary for high catalytic activity. U.S. Pat. No. 5,168,088 to Utz et al. discloses a unique way of improving the slurry catalyst dispersion during coal liquefaction by precipitating the iron oxide onto coal matrix. But it is believed that deposition by such precipitation of the entire coal feed with catalyst would present various operational problems and would also be very expensive at the commercial scale of operation.
V. Pradhan et al. disclosed in "Catalysis in Direct Coal Liquefaction by Sulfated Metal Oxides" Energy and Fuels, 1991, Vol. 5, various dispersed catalysts which have been found useful in coal liquefaction processes, including sulfated transition metal oxides such as sulfated iron oxides (Fe.sub.2 O.sub.3 /SO.sub.4) and sulfated tin oxides (Sn O.sub.2 /SO.sub.4) wherein the role of added anion (SO.sub.4.sup.2-) was attributed to the prevention of catalyst sintering or agglomeration under coal liquefaction conditions. However, further improvements are desired in catalyst forms and compositions used for hydroprocessing of various hydrocarbon feedstocks, and in the catalytic hydroconversion processes in which the catalysts are used, particularly for dispersed catalysts that are less expensive, environmentally benign, and highly active for the hydrocarbon hydroconversion processes in which they are used.